This is simple to do, but you need to have the SoundMap module (pn 1300) or the stand-alone SoundMap application.
First, measure the impulse response of the loudspeaker on a linear amplitude scale (not dB) using the time selective response algorithm. Next, select SoundMap from the ‘Offline’ menu. From the waveform dropdown menu, select ‘impulse response’ and from the analysis menu select ‘cumulative spectral decay’, then select ‘analyze’ from the actions section. If you wish, you can eliminate reflections by zooming in on the impulse before analyzing. A time-frequency map (contour plot) will be displayed.
To see a 3D waterfall plot, click on the 3D button, Various options under ‘3D axis and color’ allow you to create various log/linear views including ‘Mlssa’ type plots. For real-life examples of how this is used, see the ‘Test bench’ section in Voice Coil magazine.